Varahamihira's main work is the book Pañcasiddhāntikā (or Pancha-Siddhantika, "[Treatise] on the Five [Astronomical] Canons) dated ca. 575 CE gives us information about older Indian texts which are now lost. The work is a treatise on mathematical astronomy and it summarises five earlier astronomical treatises, namely the Surya Siddhanta, Romaka Siddhanta, Paulisa Siddhanta, Vasishtha Siddhanta and Paitamaha Siddhantas. It is a compendium of Vedanga Jyotisha as well as Hellenistic astronomy (including Greek, Egyptian and Roman elements).[4] He was the first one to mention in his work Pancha Siddhantika that the ayanamsa, or the shifting of the equinox is 50.32 seconds.

The 11th century Iranian scholar Alberuni also described the details of "The Five Astronomical Canons":

"They [the Indians] have 5 Siddhāntas:

Sūrya-Siddhānta, ie. the Siddhānta of the Sun, thought to be composed by Lāṭadeva,but actually composed by Mayasura also known as Mamuni Mayan as stated in the text itself.

Vasishtha-siddhānta, so called from one of the stars of the Great Bear, composed by Vishnucandra,

Paulisa-siddhānta, so called from Pulisa, the Greek, from the city of Saintra, which is supposed to be Alexandria, composed by Pulisa.

Romaka-siddhānta, so called from the Rūm, ie. the subjects of the Roman Empire, composed by Śrīsheṇa.

Another important contribution of Varahamihira is the encyclopedic Brihat-Samhita. It covers wide ranging subjects of human interest, including astrology, planetary movements, eclipses, rainfall, clouds, architecture, growth of crops, manufacture of perfume, matrimony, domestic relations, gems, pearls, and rituals. The volume expounds on gemstone evaluation criterion found in the Garuda Purana, and elaborates on the sacred Nine Pearls from the same text. It contains 106 chapters and is known as the "great compilation".

He was also an astrologer. He wrote on all the three main branches of Jyotisha astrology:

Brihat Jataka - is considered as one of the five main treatises on Hindu astrology on horoscopy.

Laghu Jataka - also known as 'Swalpa Jataka'

Samasa Samhita - also known as 'Lagu Samhita' or 'Swalpa Samhita'

Brihat Yogayatra - also known as 'Mahayatra' or 'Yakshaswamedhiya yatra'

Yoga Yatra - also known as 'Swalpa yatra'

Tikkani Yatra

Brihat Vivaha Patal

Lagu Vivaha Patal - also known as 'Swalpa Vivaha Patal'

Lagna Varahi

Kutuhala Manjari

Daivajna Vallabha (apocryphal)

His son Prithuyasas also contributed in the Hindu astrology; his book Hora Sara is a famous book on horoscopy. Khana (also named Lilavati elsewhere) the medieval Bengali poetess astrologer is believed to be the daughter-in-law of Varahamihir.

The Romaka Siddhanta ("Doctrine of the Romans") and the Paulisa Siddhanta ("Doctrine of Paul") were two works of Western origin which influenced Varahamihira's thought, though this view is controversial as there is much evidence to suggest that it was actually Vedic thought indigenous to India which first influenced Western astrologers and subsequently came back to India reformulated.[5] Number of his writings share similarities with the earlier texts like Vedanga Jyotisha.[6]

A comment in the Brihat-Samhita by Varahamihira says: "The Greeks, though barbarians.,[7] must be honored since they have shown tremendous interest in our science....." ("mleccha hi yavanah tesu samyak shastram kdamsthitam/ rsivat te 'p i pujyante kim punar daivavid dvijah" (Brihat-Samhita 2.15)).

Among Varahamihira's contribution to physics is his statement that reflection is caused by the back-scattering of particles and refraction (the change of direction of a light ray as it moves from one medium into another) by the ability of the particles to penetrate inner spaces of the material, much like fluids that move through porous objects.[12]

1. ^ "the Pañca-siddhāntikā ("Five Treatises"), a compendium of Greek, Egyptian, Roman and Indian astronomy. Varāhamihira's knowledge of Western astronomy was thorough. In 5 sections, his monumental work progresses through native Indian astronomy and culminates in 2 treatises on Western astronomy, showing calculations based on Greek and Alexandrian reckoning and even giving complete Ptolemaic mathematical charts and tables. Encyclopædia Britannica (2007) s.v.Varahamihira ^

^"the Pañca-siddhāntikā ("Five Treatises"), a compendium of Greek, Egyptian, Roman and Indian astronomy. Varāhamihira's knowledge of Western astronomy was thorough. In 5 sections, his monumental work progresses through native Indian astronomy and culminates in 2 treatises on Western astronomy, showing calculations based on Greek and Alexandrian reckoning and even giving complete Ptolemaic mathematical charts and tables. Encyclopædia Britannica (2007) s.v.Varahamihira

^History of astronomy in India. Indian National Science Academy. p. 85, 114, 345.